Identification of allergen components of the opportunistic yeast Pityrosporum orbiculare by monoclonal antibodies.

The yeast Pityrosporum orbiculare (P. orbiculare) is a member of the normal human cutaneous flora, but it is also associated with several clinical manifestations of the skin. We have previously observed IgE-binding components in P. orbiculare extracts, using sera from patients with atopic dermatitis. In the present study, we raised several monoclonal antibodies (MoAbs) against P. orbiculare to characterize some of its antigens, and used Candida albicans (C. albicans) as a control. We obtained several IgG1 MoAbs which specifically recognized P. orbiculare in ELISA. Two of these were selected for immunoblotting studies on P. orbiculare, and two patterns of reactivity emerged. Firstly, one MoAb showed a distinct band at a molecular mass of 67 kDa. In the second pattern, a sharp band at about 37 kDa appeared. In contrast, the IgM antibodies raised reacted with a 14-kDa component; but they reacted with C. albicans in addition to P. orbiculare. The IgG1 antibodies seemed to react with proteins, as their ability to react in ELISA with extract pretreated with protease was greatly reduced. In contrast, IgM MoAbs were much less affected, suggesting that they recognized nonprotein components. To determine whether these MoAbs-binding components were also recognized by human IgE, we adopted a radioimmunoassay (RIA) using the MoAbs as catcher antibodies. Both the 67-kDa and the 37-kDa components were IgE-binding proteins. P. orbiculare RAST positive sera were scored as positive in the RIA, whereas the control serum was not.